In the prior art, room temperature-curable organopolysiloxane compositions are widely used as sealing agents or the like. Prior to curing, they are liquid or pasty and thus tacky to the worker hands so that manual operation is substantially prohibited.
Adhesives and sealing agents in putty form are also known in the art. Among others, silicone putties using organopolysiloxanes as base polymers are well known. As compared with other organic rubbers, silicone putties have good heat resistance and freeze resistance and maintain stable rubber physical properties and electrical properties even at elevated temperatures or in a hot humid environment, and thus used in a variety of applications including electric, electronic, automotive and building industries. In particular, silicone putties endowed with a curing ability are used as shape-forming, dental impression and building sealing materials and find many other applications.
These puttylike curable silicone compositions are generally formulated by compounding a polyorganosiloxane as a base polymer with a filler for imparting a putty form prior to curing such as fumed silica, finely divided quartz, calcium carbonate, diatomaceous earth and aluminum silicate, and optionally adding a curing or curing agent for imparting curing ability. In order that these compositions be endowed with a putty form, made tack-free to the hands or fingers and effectively worked, the viscosity of the base polymer and the type and quantity of the filler must be carefully selected. Otherwise, the properties of the cured product are substantially limited.
JP-A 63-10662 discloses a puttylike silicone composition comprising a polyorganosiloxane and a polymethylsilsesquioxane. However, the polymethylsilsesquioxane is a non-elastic resin and has a durometer hardness of at least 90 as measured by the JIS Type A durometer hardness test. When the polymethylsilsesquioxane is compounded in a curable silicone composition, the rubber as cured lacks flexibility due to an increased hardness and has poor adhesion and sealing tightness. JP-A 10-511730 discloses a sealing composition comprising a high viscosity oil as a base polymer, which composition is self-supporting prior to curing. JP-A 11-61100 and JP-A 11-106738 disclose sealing compositions comprising a high molecular weight gum-like base polymer and fumed silica. All these compositions are unsatisfactory in ease of working and rubber elasticity.